The present invention relates to a novel modular fixture to be used in an apparatus for coating workpieces and to a process for coating said workpieces. The present invention has particular utility in the coating of vanes and blades for industrial turbines and jet engines.
Vanes and blades used in industrial turbines and jet engines are typically subjected to a coating operation to improve their resistance to corrosion, thermal fatigue, and to otherwise enhance their performance. Economic concerns dictate that one must be able to simultaneously coat multiple workpieces in order to have a commercial process.
One commercial system for simultaneously coating a plurality of workpieces is shown in U.S. Pat. No. 4,192,253. In this system, a plurality of workpieces to be coated are inserted into a coating chamber and simultaneously rotated about their longitudinal axes during the coating operation. The simultaneous rotation of the workpieces about their longitudinal axes is accomplished by mounting each workpiece to the tip of a fixture whose other end is connected to a complex gear operated drive system for rotating the fixture and the individual workpieces mounted thereto. This type of system is disadvantageous for a number of reasons. For example, the system is complex and potentially troublesome from a maintenance standpoint. Still further, the costs associated with such a system are quite high. Yet, another disadvantage is the delay incurred in individually removing the coated workpieces from each of the fixtures and mounting new workpieces to be coated onto the fixtures.
More recently, it has been proposed to coat multiple workpieces at a single time using a modular fixture arrangement. This type of coating system is illustrated in copending U.S. patent application Ser. No. 08/782,398, filed on Jan. 13, 1997, to John W. Menchetti et al., entitled MODULAR COATING FIXTURE, and assigned to the Assignee of the present application.
Certain coating techniques, such as electron beam physical vapor deposition, are line of sight techniques wherein surfaces of a workpiece which are not in a line of sight with the source of the coating material will not be coated. Thus, there still remains a need for an apparatus and process which enables one to coat surfaces, such as platforms, which are perpendicular or near perpendicular to other surfaces of a workpiece to be coated.